Silver halide emulsions or developers containing a hydrazine compound are disclosed in U.S. Pat. No. 3,730,727 (a developer containing ascorbic acid and hydrazine), U.S. Pat. No. 3,227,552 (use of hydrazine as an auxiliary developing agent for obtaining direct positive color images), U.S. Pat. No. 3,386,831 (a silver halide photographic material containing a .beta.-monophenylhydrazide of an aliphatic carboxylic acid as a stabilizer therefor), U.S. Pat. No. 2,419,975 and Mees, The Theory of Photographic Process, 3rd edition, page 281 (1966).
In particular, U.S. Pat. No. 2,419,975 discloses that high contrast negative images are obtained by the addition of hydrazine compounds. The aforesaid patent describes that very high contrast photographic characteristics are obtained by adding a hydrazine compound to a silver chlorobromide emulsion and developing it with a developer having a high pH of 12.8. However, the strong-alkaline developer having a pH of about 13 is unstable because it is easily air-oxidized and can not endure long-term storage and use.
Very high contrast photographic characteristics having a gamma (.gamma.) over 10 are very useful for the photographic reproduction of continuous tone images by dot images useful for making printing plates or the reproduction of line images. For such a purpose, a process of using a silver chlorobromide photographic emulsion having a silver chloride content of over 50 mole %, and more preferably over 75 mole % and developing it with a hydroquinone developer having a very low effective concentration (usually lower than 0.1 mole/liter) of sulfite ion is generally used. However, since in the aforesaid process, the sulfite ion concentration of the developer is low, the developer is very unstable and can not endure storage for over 3 days.
Furthermore, since the aforesaid process requires the use of a silver chlorobromide emulsion having a relatively high silver chloride content, the process can not give high sensitivity. Accordingly, it has been strongly desired to obtain high contrast photographic characteristics useful for the reproduction of dot images and line images using a high speed silver halide emulsion and a stable developer.
The present inventors have found that the acylhydrazine compounds used for silver halide photographic emulsions giving very high contrast negative photographic characteristics using a stable developer disclosed in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,243,739, 4,272,614, 4,323,643, etc., have various defects.
For example, it is known that these conventional hydrazines generate nitrogen gas during development which forms bubbles in the photographic film during processing to damage the photographic images formed. Furthermore, the hydrazine compounds flow out into the developer solution during processing which adversely affect the quality of the other photographic materials.
Also, these prior art hydrazines are required to be used in a large amount thereof to obtain high sensitivity and high contrast. Further, when the hydrazine is used in combination with other sensitizing techniques (e.g., enhancing a chemical sensitivity, enlarging grain size or, adding compound accelerating sensitization as described in U.S. Pat. Nos. 4,272,606 and 4,241,164) in cases where a particularly high sensitivity is required in regard to the performance of photographic light-sensitive materials, the sensitization with the passage of time and the formation of fog by sensitization generally occur during the storage of the photographic light-sensitive materials.
Accordingly, compounds capable of reducing the generation of bubbles and their flow into a developer, giving no problem in long-term storage stability, and capable of giving very high contrast photographic characteristics by the addition of a very small amount thereof are desirable.
Also, it is disclosed in U.S. Pat. Nos. 4,385,108, 4,269,929 and 4,243,739 that very high contrast negative gradation photographic properties are obtained by using hydrazines containing a substituent capable of easily adsorbing onto silver halide grains. However, some of these hydrazines having the adsorptive substituent group cause the desensitization with the passage of time during the storage of the photographic light-sensitive materials containing the compounds. Accordingly, it is required to select hydrazine compounds that do not cause this problem.
On the other hand, there are various direct positive photographic processes, and among them, a process of light-exposing a silver halide emulsion containing previously fogged silver halide grains in the presence of a desensitizer and then developing the emulsion and a process of light-exposing a silver halide emulsion having sensitive specks mainly in the silver halide grains and then developing the emulsion in the presence of a nucleating agent are most useful. The present invention relates to photographic light-sensitive materials for use in the latter process. The aforesaid silver halide emulsion having sensitive specks mainly in the interior of silver halide grains and forming latent images mainly in the interior of the silver halide grains is referred to as "internal latent image type silver halide emulsion" and shall be distinguished from a silver halide emulsion forming latent images mainly on the surface of the silver halide grains.
A process of obtaining direct positive image by surface-developing the internal latent image type silver halide photographic emulsion in the presence of a nucleating agent and silver halide photographic emulsions and photographic light-sensitive materials which are used for the process are known.
In the aforesaid process of obtaining direct positive images, the nucleating agent may exist in the developer. However, when the nucleating agent is incorporated in either the silver halide photographic emulsion layer or other proper layer of the photographic light-sensitive material and adsorbed on the surface of the silver halide grains therein, good reversal characteristics can be obtained.
As the nucleating agent which is used for the aforesaid process of obtaining direct positive images, there are hydrazine and hydrazine series compounds described in U.S. Pat. Nos. 2,563,785 and 2,588,982; hydrazide and hydrazine series compounds described in U.S. Pat. No. 3,227,552; heterocyclic quaternary salt compounds described in U.S. Pat. Nos. 3,615,615, 3,719,494, 3,734,738, 4,094,683 and 4,115,122, British Patent 1,283,835, Japanese Patent Application (OPI) Nos. 3426/77 and 69613/77 (the term "OPI" as used herein indicates an "unexamined published application"); thiourea bond-type acylphenylhydrazine series compounds described in U.S. Pat. Nos. 4,030,925, 4,031,127, 4,139,387, 4,245,037, 4,255,511 and 4,276,364, and British Patent 2,012,443; compounds gaving a heterocyclic thioamide as an adsorptive group described in U.S. Pat. No. 4,080,207; phenylhydrazine compounds having a heterocyclic group having a mercapto group as an adsorptive group described in British Patent 2,011,397; sensitizing dyes having a substituent showing a nucleating action in the molecular structure thereof described in U.S. Pat. No. 3,718,470, and hydrazine compounds described in Japanese Patent Application (OPI) Nos. 200230/84, 212828/84, and 212,829/84, and Research Disclosure, No. 23510 (November, 1953).
However, it has been confirmed that these compounds have the following disadvantages. That is, some of these compounds are insufficient in activity as nucleating agent; some of the compounds are insufficient in storage stability although the activity is high; some of the compounds decrease the activity thereof after being added to a silver halide emulsion and before coating; also, some of the compounds deteriorate the layer quality when a large amount thereof is added to the emulsion layer.
For solving the aforesaid problems, hydrazine derivatives such as adsorption-type hydrazine derivatives, etc., are proposed in Japanese Patent Application (OPI) Nos. 179734/85, 170733/86, 65034/87, and 270744/86 and Japanese Patent Application No. 19,739/85 and a considerable improvement has been achieved by using these hydrazine derivatives. However, the activity as nucleating agent is insufficient for the requirement of lowering the pH of a developer for increasing the stability of the developer (i.e., preventing the deterioration of the developing agent in the developer) or shortening the developing time.